How to use the online timer
Children respond to a visible countdown far better than to a repeated instruction, largely because a number that is going down is concrete in a way that soon and five more minutes are not. It also changes who is enforcing the limit. The timer becomes the thing that says stop, which removes a good deal of the daily friction between a child and the adult who would otherwise have to say it again.
These pages cover the moments where that structure genuinely helps: brushing for the two minutes the NHS recommends rather than the forty seconds most children manage, homework blocks sized for a primary-age attention span, screen time with an agreed end, and a bedtime story where the point is as much the shared attention as the book. Durations run shorter than the adult equivalents, because that is what is realistic rather than what would be convenient.
Start the timer before the activity rather than partway through, and give a warning before it ends. Nearly all the trouble with limits comes from the abrupt stop rather than from the length, and a limit that stays the same from one day to the next stops being tested within a fortnight.